iio: adc: sc27xx: Use devm_hwspin_lock_request_specific() to simplify code

Change to use devm_hwspin_lock_request_specific() to help to simplify the
cleanup code for drivers requesting one hwlock.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>